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Full text of "The Morphology And Evolution Of The Apes And Man"

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 THE SKELETON AND TEETH             123
The suture between the basi-occiput and basi-sphenoid is sinuous. Its width decreases as age advances, till there is no trace present in old animals. In all skulls examined by me there is a small foramen in the basisphenoid.
The median vertical occipital crest varies in prominence with age and sex. Thus it is small in the immature male, large in the adult male and sma.ll or absent in the adult female.
On making a vertical section through the skull the air-sinuses which excavate some of the bones make their appearance (fig. 47). The frontal sinuses (F.P.i are narrow and communicate with the inferior meatuses of the nose by the naso-lachrymal ducts. The sphenoidal sinus (S.S.) is large, undivided and excavates deeply into the alisphenoids; it communicates with the postero-superior part of the nasal fossa. When the turbinate bones are removed the antrura of Highrnore makes its appearance. It is an irregular cavity with buttresses projecting into it; and its floor has elevations produced by the sockets of the incisor, molar and canine teeth. Xo mastoid antrum is present.
When the calvarium is removed the cranial cavity appears ovoid in outline, with the narrow end anterior. The anterior fossa is considerably reduced by the convex roofs of the. orbits. Between the orbits there is a deep fossa, at the bottom of which the cribriform ethmoid plate is very obvious. There is a slight median antero-posterior crest on the cribriform plate, but no marked crista galli is present.
The lateral parts of the middle cranial fossa are deep towards their medial parts. The anterior clinoid processes are well marked, but are situated some distance